Impact of electron exchange and correlation to simulate the structure, electronic and nonlinear optical properties of urea

2015
Volume 14
Issue 1
King Khalid University Journal of Basic and Applied Sciences

In the present investigation, the efficiency of different quantum chemical methods including a range of electron exchange and correlation has been checked to simulate the molecular structure, electronic and nonlinear optical properties of urea. Different quantum chemical methods including semi-empirical with no exchange and correlation (AM1 and PM3), ab initio with static and dynamic correlation (HF, MP2 and CCSD) and density functional theory (B3LYP and PBE0) methods having exchange and correlation effects, have been applied to calculate geometrical, electronic and nonlinear optical properties of urea. The obtained results at different methods have been compared with highly accurate and correlated CCSD method to check the effect of electron correlation. The results show that for molecular geometry optimization, B3LYP functional (with 15 % of HF exchange) is found to be computationally 25 times less expensive and shows good agreement with CCSD geometrical parameters. For polarizability properties including dipole moment (μz), polarizability (αzz), and first hyperpolarizability (βzzz), MP2 and B3LYP methods have reproduced the CCSD values, which indicates that exchange and correlation effects are important to accurately model the electronic and nonlinear optical properties of small organic molecules like urea. While for vertical ionization potential (VIP), vertical electron affinity (VEA), and chemical hardness (η), HF and MP2 results are close to highly correlated CCSD results. Thus the present study provides the fundamental insights into the parent organic molecule of urea by spotlighting the impact of exchange and correlation effect on the modeling of its structure-property relationship.

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